# Logic - What does a half T mean in logic?

TLDR nevermind I'll include a screenshot;

I've looked for the symbol everywhere, it wasn't even found via wikipedia: https://en.wikipedia.org/wiki/List_of_logic_symbols

It also wasn't in the list of mathematical symbols: https://en.wikipedia.org/wiki/List_of_mathematical_symbols

There's a section called 'advanced and rarely used logical symbols' in the wiki page for logic, and it's not even there. So that is officially the point at which I give up.

I don't mean the symbols for True, T. The stem of the T by the way, remains untouched, it's just that the left side is 'cut off'.

Also, I would copy and paste the damn thing, but it's always added in via a super special way, and it just turns out like this: f Γ. So yeah.

• You could take a screen shot or screen clip.
– Em.
May 29, 2016 at 9:52
• Oh yeah good idea May 29, 2016 at 9:53
• That's a capital gamma. Usually used for a set of formulae.
– Ori
May 29, 2016 at 9:56
• Do people really use that in logic? Presumably it's not in common use. May 29, 2016 at 9:58
• It depends on your course, but from what I've seen, it's fairly common. Greek letters are often used in mathematics, and Logic is no exception.
– Ori
May 29, 2016 at 10:01

In Sequent Calculus discussions, capital greek letters such as $\Gamma, \Delta, \Sigma,$ and $\Pi$, are often used as symbols for finite sets of first order predicate logic formula.   (Pronounced "gamma", "delta", "sigma", and "pi".)

https://en.wikipedia.org/wiki/Sequent_calculus#Inference_rules

In this case the rule of implication introduction, means that "if some set of formula and $A$ entails $B$, then that set of formula entails that $A$ implies $B$." $${\begin{array}{rcl}\Gamma, A & \vdash & B \\\hline \Gamma&\vdash&A\to B\end{array}}{\small{\to}\mathsf I}$$

• Oh cool, presumably the only elements are propositions? May 29, 2016 at 14:11
• @user2901512 $\Gamma$ is some set of well-formed formula of propositions and logical connectives. May 29, 2016 at 14:21

As others have pointed out, your "$T/2$" is the upper-case Greek letter gamma.

For the record, as I can't find it anywhere else on MSE, here is the Greek alphabet as supported by MathJax and $\LaTeX$ and used throughout mathematics. The format is:

$$\begin{array}{llll} \mbox{Name} & \mbox{Upper-case glyph} & \mbox{Lower-case glyph} & \mbox{Variant glyph (if any)}. \end{array}$$

Use \Name for the upper-case letter and \name for the lower-case letter. Letters with a superscript 1 (like $A^1$) look like Latin letters, so they aren't useful as mathematical symbols and $\LaTeX$ and MathJax don't have a macro for them (you could try to defend notation like $H(H)$ by claiming that the second $H$ is an upper-case eta, but this is probably not going to make you popular $\ddot{\smile}$). Letters with a superscript 2 (like $\varphi^2$) are a variant lower-case form: use \varname for these.

$$\begin{array}{llll} \mbox{Alpha} & A^1 & \alpha \\ \mbox{Beta} & B^1 & \beta \\ \mbox{Gamma} & \Gamma & \gamma \\ \mbox{Delta} & \Delta & \delta \\ \mbox{Epsilon} & E^1 & \epsilon & \varepsilon^2 \\ \mbox{Zeta} & Z^1 & \zeta \\ \mbox{Eta} & H^1 & \eta \\ \mbox{Theta} & \Theta & \theta \\ \mbox{Iota} & I^1 & \iota \\ \mbox{Kappa} & K^1 & \kappa \\ \mbox{Lambda} & \Lambda & \lambda \\ \mbox{Mu} & M^1 & \mu \\ \mbox{Nu} & N^1 & \nu \\ \mbox{Xi} & \Xi & \xi \\ \mbox{Omicron} & O^1 & o^1 \\ \mbox{Pi} & \Pi & \pi \\ \mbox{Rho} & P^1 & \rho \\ \mbox{Sigma} & \Sigma & \sigma & \varsigma^2 \\ \mbox{Tau} & T^1 & \tau \\ \mbox{Upsilon} & \Upsilon & \upsilon \\ \mbox{Phi} & \Phi & \phi & \varphi^2 \\ \mbox{Chi} & X^1 & \chi \\ \mbox{Psi} & \Psi & \psi \\ \mbox{Omega} & \Omega & \omega \end{array}$$